Robots are being developed that walk by changing the relative postures among the left leg link, the hip, and the right leg link. When the relative postures among the left leg link, the hip, and the right leg link are to be changed, the relative postures among the left leg link, the hip, and the right leg link must be changed so that the robot can walk as a result. For this purpose, gait data is used that indicates the positions and postures of the left foot tip, the hip, and the right foot tip respectively.
As shown in FIG. 10, the gait data indicates the positions and postures of the left foot tip, the hip, and the right foot tip respectively in a global coordinate system that defines the coordinates of the space in which the robot is to move. In order to indicate the positions of the left foot tip, the right foot tip, and the hip, a reference point L0 is established for the left foot tip, a reference point R0 is established for the right foot tip, and a reference point W0 is established for the hip. In order to indicate the postures of the left foot tip, the right foot tip, and the hip, a reference vector L is established that is perpendicular to the left foot tip, a reference vector R is established that is perpendicular to the right foot tip, and a reference vector W is established that extends along the hip column. In the global coordinate system, the gait data indicates the x, y, z coordinates of the reference point L0 of the left foot tip, the x, y, z coordinates of the reference point R0 of the right foot tip, and the x, y, z coordinates of the reference point W0 of the hip. In addition, the gait data indicates the pitch angle Lα, the roll angle Lβ, and the yaw angle Lγ of the reference vector L, the pitch angle Rα, the roll angle Rβ, and the yaw angle Rγ of the reference vector R, and the pitch angle Wα, the roll angle Wβ, and the yaw angle Wγ of the reference vector W. The gait data chronologically records data that indicates the positions and the postures of the left foot tip, the right foot tip, and the hip. In FIG. 10, the pitch angle Vα, the roll angle Vβ, and the yaw angle Vγ of the vector V is illustrated.
When gait data that indicates the positions and postures of the left foot tip, the right foot tip, and the hip, are given, the robot will calculate the joint angles of joints needed to take the given positions and given postures, and will adjust joint angles of the joints to be equal to these calculated joint angles. Because the gait data is chronologically changed, the joint angles will also be chronologically changed. The robot will walk by chronologically changing the relative postures between the left leg link, the hip, and the right leg link in accordance with the gait data. The robot will continue walking without tipping over because the positions (Wx, Wy, Wz) and postures (Wα, Wβ, Wγ) of the hip are calculated to satisfy a relationship that ZMP (zero moment point) of the robot will remain within the foot plane of the leg that is in contact with the ground. The aforementioned method can be said to be a method of actively changing joint angles of all of the joints of the robot in order to walk, and is disclosed, among other places, in Japanese Laid-Open Patent Application Publication H05-253867.
The present inventors have been performing an intensive study of walking technology that is different from the technology described above, and in which some of the joints angles of the robot are passively changed and the robot walks with natural movement. In an application that precedes the present application (Japanese Laid-Open Patent Application Publication 2004-276167), a robot and a control method thereof are disclosed in which the robot will perform natural and stable stepping movements within a lateral plane and draw the idle leg forward in association with the circle of stepping within the lateral plane. The robot will walk with natural movement. With the aforementioned technology, the ankle joint of the grounded leg of the robot pivots freely, the joint angle of the ankle joint is measured, and joint angles of the remaining joints of the robot are adjusted based upon the measured joint angle of the ankle joint of the grounded leg. The joint angles of the remaining joints are adjusted so that the center of gravity of the robot moves toward a position at which the idle leg link will be grounded. With the aforementioned technology, a robot walks with a natural and passive movement because the ankle joint of the grounded leg of the robot can rotate freely and naturally.
By employing the aforementioned technology, the robot steps with a natural movement while walking. Because inertia and gravity that act upon the robot are effectively used to achieve the aforementioned stepping movements, a robot is capable of walking with less energy than when all joints thereof are actively moved.